This invention relates to thrust bearing assemblies and more particularly to vibration reducing, self-aligning thrust bearing assemblies used in large capacity marine propulsion systems.
Various thrust bearing arrangements have been proposed for reducing vibration and misalignment problems occurring during transmission of thrust loads in marine propulsion systems. For example, hydrodynamic or "Kingsbury" pivoted-pad type of bearing assemblies are widely employed in large marine vessels to transmit forward and aft thrust loads from a propulsion shaft to the thrust bearings and ultimately to the hull structure. A "Kingsbury" bearing commonly includes a stationary housing surrounding the shaft, a radially projecting thrust flange formed on the shaft, and forward and aft bearing pads positioned between the thrust flange and the housing. A plurality of hydraulically supported piston elements have been used between the forward and aft bearing pads and the bearing housing to more uniformly distribute thrust forces applied to the housing. Further, propeller induced vibrations are reduced by the damping properties of the hydraulic fluid and other design provisions of the hydraulic system supporting such pistons. However, "Kingsbury" type hydraulic thrust bearings have common disadvantages in requiring somewhat greater starting torques than other types of bearing assemblies and having reduced piston life due to galling and seal wear in the piston assemblies. Such seal wear and piston galling are caused by shaft misalignment and uneven bearing pressure distribution, which also reduces the effectiveness of the piston as a vibration reducer.
Roller bearings have been used in various marine bearing assemblies to lower the starting and frictional torque characteristics of a selected bearing assembly. However, misalignment of the bearings often imposes various sliding motions in the bearings themselves, which tends to reduce the bearing life. To overcome reduced bearing life encountered with these bearings, tapered roller bearings have been employed, as exemplified by U.S. Pat. No. 3,826,544 granted to Anderson.
The thrust bearing assembly constructed according to the present invention is designed to overcome various problems encountered with the prior art, such as reduced piston wearability. For example, an annular piston of the present invention is uniformly supported in a fluid cavity to reduce the effects of concentrated and eccentric thrust loads placed on the bearing elements, even where the shaft and its bearing flange are misaligned with respect to the housing.